1. Field of the Invention
The present invention relates to an injection moulding process for the manufacture of multi-layered articles, and especially to the manufacture of multi-layered containers having barrier properties.
2. Description of the Prior Art
A wide variety of polymers may be used in injection moulding processes e.g. polyolefins, especially polyethylene, polypropylene and ethylene/vinyl acetate copolymers, polyesters and polyamides. As used herein, polyethylene refers to homopolymers of ethylene and copolymers of ethylene with minor amounts of at least one C.sub.4 -C.sub.10 hydrocarbon alpha-olefin.
A particularly important end-use for polyolefins is in the packaging industry, for instance in the injection moulding of polyethylene to form articles, especially containers. Polyethylene used in injection moulding processes may exhibit melt indices in the range of about 0.3 to 120 dg/min, or even higher, depending on the intended end-use of the resultant article and the physical characteristics required in the article. Melt index is inversely related to molecular weight and is measured by the procedure of ASTM D-1238 (Condition E).
Polyolefins exhibit excellent resistance to permeation by water, which may be a useful property in packaging end-uses. However, polyolefins tend to be very permeable to gases and some liquids, especially oxygen and hydrocarbon liquids, and such characteristics may limit the usefulness and acceptability of polyolefins as a packaging material, especially in the packaging of materials, e.g. foodstuffs, susceptible to, for example, the effects of oxygen.
It is well known in the packaging industry to form laminated and co-extruded structures, especially packaging films. Such structures may have a number of layers, and each layer may be intended to impart particular properties to the structure. For example, the structure may contain layers intended to be impermeable to water, oxygen, carbon dioxide, fats and oils and the like. Multi-layer structures in the form of, in particular, film and bottles, and/or processes for the manufacture thereof, are disclosed in U.S. Pat. Nos. 3,857,754 and 3,975,463, both of S. Hirata et al., which issued Dec. 31, 1974 and Aug. 17, 1976 respectively, and in U.S. Pat. Nos. 4,410,482 and 4,444,817, both of P. M. Subramanian, which issued Oct. 18, 1983 and Apr. 24, 1986, respectively.
A process for the manufacture of hollow bodies having a three layer structure is disclosed in published European patent application 0 075 816 of P. Bauer and J. Schmidtchen, published Apr. 6, 1983. The process comprises placing a two-layer laminate in a mould of a blow-moulding process, and then laminating the third layer by means of the parison of the blow moulding process. The two-layer laminate may be, for instance, aluminum foil, copper foil, polyvinyl chloride, polyvinylidene chloride or polyamide laminated to a thermoplastic adhesive e.g. ethylene/acrylic acid copolymer or ethylene/vinyl acetate copolymer. The polymer of the parison is a polyethylene having a density of 0.935-0.965 g/cm.sup.3 and a melt index of 0.01-2 dg/min.
Injection moulding processes for the manufacture of articles having labels as an integral part of the article are disclosed in, for example, Canadian Patent 1 031 527 of E. Lind, which issued May 23, 1978 Japanese patent application 60 012 244 of Yuka Goseishi KK, published Feb. 2, 1985 and Japanese patent application 58 069 015 of Yuka Goseishi KK, published Apr. 25, 1983. The manufacture of electrically shielded cabinets by injection moulding a molten polymer into a mould containing a metal foil e.g. aluminum, coated with a hot melt adhesive is disclosed in Japanese patent application 52 047 057 of Hitachi KK, published Apr. 14, 1977. The injection moulding of a substrate layer e.g. polystyrene, with a metallized layer and a protective layer e.g. polyester, is disclosed in U.S. Pat. No. 3,839,129 of H. G. Neumann, which issued Oct. 1, 1974.